The present invention relates to incentive spirometers of the type wherein an object is caused to rise in a transparent tube in response to inhalation through the tube by a patient. Incentive spirometers of this general type are well known in the prior art, as shown by U.S. Pat. Nos. 4,182,347; 4,183,361; 4,170,228; 4,114,607; 4,086,918; 4,025,070; and others. In addition, a prior art incentive spirometer of this type is illustrated and described in U.S. Patent Application Ser. No. 247,097, filed Mar. 24, 1981 now U.S. Pat. No. 4,391,283, by Edward N. Sharpless, Marvin Gordon and Joseph Lichtenstein, and bearing the title "Improved Incentive Spirometer", which patent application is expressly incorporated in its entirety herein by reference.
Incentive spirometers of this type have a common problem which results in an inaccuracy of the monitoring of the breathing exercise. Specifically, the tube in which the incentive member is caused to rise by inhalation should be maintained vertical so as to minimize frictional interaction between the incentive member and the inside wall of the tube. However, in use, it is common for the incentive spirometer to be placed next to the patient on a bed or other surface which is not necessarily level. When the supporting frame for the incentive spirometer tilts, the inhalation tube likewise tilts so that the desired vertical orientation is destroyed. Moreover, in some instances, the patient will support the frame in his or her hands and will inadvertently cause the frame to tilt with the same undesirable result.